As a younger railfan, I have a guess to why certain railfan activities that might rely more on nostalgia might be declining - there's simply less nostalgia to be expressed.

The oldest railfans can remember a lot of changes over the years - the end of steam, the end of private passenger service, the end of heaveyweights, the plethora of fallen flags. Recreating these things through modelling probably has more value to people who have direct memories of those days when streamliners or steam engines roamed the earth.

All of these things happened before I could have paid any attention, with the last big round of mergers being when I was five or six. Things have been visually stable for most of my life - it's the same old freight trains in the same old paint with the same old autoracks or intermodal cars that I always remember them hauling, with the occasional same old' Amtrak trailing behind the same coaches it's been pulling for 40 years. There's more trains going down the tracks, perhaps, but they're fundamentally what they've always been to me.

As for the rest, I agree with the theory that younger people today have better access to information than monthlies can provide